A wedge of this nutty and citrusy shortbread is a light finish to a meal.
Preheat oven to 350 degrees, with racks in upper and lower thirds. Place the hazelnuts on a rimmed baking sheet in a single layer; toast in upper rack of oven, shaking occasionally, until skins begin to split, about 15 minutes. Remove from oven (leave oven on); immediately rub hazelnuts vigorously in a clean kitchen towel to remove skins (as much as will come off easily). Let cool.
Finely chop hazelnuts in a food processor (do not overprocess), about 20 seconds. Transfer chopped nuts to a large bowl, and add flour, granulated sugar, melted butter, zest, and the salt. Mix with hands until dough just comes together and forms a ball.
Line two rimmed baking sheets with parchment paper. Divide dough in half. Shape each piece into a disk; transfer each disk to a lined baking sheet. With lightly floured hands, flatten one piece into a 7-inch round.
Score round to divide into 12 equal wedges (do not cut all the way through). Sprinkle round with 1 tablespoon sanding sugar. Repeat with remaining disk.
Bake shortbread in upper and lower thirds of oven, switching positions of sheets and rotating halfway through, until rounds are golden brown, 15 to 20 minutes. While shortbread is still warm, cut wedges to fully separate. Let wedges cool slightly on sheets, then transfer to a wire rack to cool completely.